2-stroke 25HP mercury stalls while accelerating.

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Jay415

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Just bought a 1999 2-stroke 25HP ELH Mercury motor. Run pretty good but I think it might need some carb work. I changed the plugs, cleaned the gas filter, and used fresh gas with ethanol treatment and mercury synthetic 2cycle oil, 50:1. Motor starts right up and seems to idle fine. It'll will putt along slowly so so, but once you give it gas to accelerate it want to stall. I have to play with the choke a little to get it to accelerate. Once I get passed that I can adjust throttle from 1/4 throttle to Wide open and back and forth with no problems or bogging. Once I slow to an idle and try to accelerate again it starts bogging. I though maybe the idle was too low so I turned the idle adjustment screw slightly but it sounds like its idling a little too fast and it hasn't helped, still the same bogging when accelerating. Plus now it's slamming into gear harder. The motor was very clean and sitting around for a while. Am I thinking right, that is must be a carb issue? What should I do to remedy this?
 
Sounds like the high speed jet is plugged.. By pulling the choke, your fooling the carb into giving more fuel by cutting off the air.
Float level may need adjustment and cleaning too.

On the other hand, you say that after you get past 1/4 throttle it seems ok.. Perhaps the timing is off.. Don't ask me how to link and sync though.. Never had that problem yet!
 
I am doing a seafoam treatment hoping it will clean the carb enough to solve the problem. Here's a short video of how it's running. With the hose hooked up with muffs I can put it in gear and rev it no problem. Not sure if the seafoam helped or if it's because the motor isn't under a load.

[youtube]z7Q1uD6UBYs[/youtube]
 
I had the same problem with my 115 but it's Efi so I had to replace the high pressure fuel screen and now it runs like a top!

I'm going with the high speed jet on this one. Carb rebuilds are simple and pretty easy if you know what not to do
 
Haha can you list the what not to do's?? Lol I am pretty good mechanically so I don't mind attempting it. I need to find a service manual also. The question is do I have all the right tools.
 
Jay415 said:
Haha can you list the what not to do's?? Lol I am pretty good mechanically so I don't mind attempting it. I need to find a service manual also. The question is do I have all the right tools.


1. Have a clean desk
2. Have a gallon of Chem dip from your local autozone
3. Always put your parts in a line and go from left to right as you remove them, that will tell you what part goes next.
4. Buy a can of Silikroil for tight bolts
5. Buy a can of carb cleaner
6. Count the turns exactly when removing the jet pins. You will need to write this down. One is a low jet, the other is a high jet. Go in 1/2 turns down until it bottoms out. Then write down how many turns and remove it completely.

After everything is removed place your carb in the Chem dip carburetor cleaner for 24 hours. This will remove any sediment buildup and clean it up.

Now onto installing new parts.
1. Go from right to left from your removed parts and line up your new parts exactly.
2. Install the new parts in succession until it is complete.
3. Once it is complete Turn your jet pins all the way out and slowly count the turns out. If you mess up its ok just go back down and retry. There might be a 1/4 turn in the end depending on how it's set.

Install the carb and start your engines. Tune in 1/4 increments until it purrs like a kitten.

The Silikroil is worth it's weight in gold. Use it on any bolts that are stubborn. Spray it and let it sit for a few minutes. I recommend spraying all outside bolts with it and let it sit for an hour before starting the rebuild.

I hope this helps
 
As for the tools it's pretty simple small shop screws, maybe a set of hex keys. Look to see if your carb needs any special tools, most don't but you never know.

The biggest point is a completely clean cleared shop desk that's been wiped down to remove any dirt or dust. Cleanliness is probably the biggest thing on this one.

Microfiber shop towels are really nice also!
 
Thanks I think I'll order a carb rebuild kit and give it a try. I have plenty of tools just wasn't sure if I'd need any special testing equipment. I'm sure I won't have any problem.
 
It wouldn't be a bad idea to pick up a pop off pressure tool

I use a mighty vac MV8000

ImageUploadedByTapatalk1342736424.261094.jpg

If you are just rebuilding and not messing with it just install the same color or size spring that you remove and the pop off tool wouldn't be needed.

The mv8000 is also a vacuum pump so I've used it many times on multiple applications from fuel vacuum testing for air pockets to sucking lube out of the foot of your engine for replacement!

Really handy tool.

When you do the rebuild the kit will have everything you need and instructions for doing the rebuild. But the pump is just friggin handy.
 
Cool thanks for the info. I went to crowleymarine.com I now need to figure out the model number for my motor. It's not I'm the sticker. I thought I would just look it up by the year and 25 HP ELH.
 
There should be a manufacturing sticker on the right side of the motor when you are standing from the rear. It should say your year, cc displacement, and a few numbers.

Also the two bar codes on the side of the engine has numbers. Just write them down also for searching boats.net
 
I have to look again when I get home but the sticker your talking about doesn't have a model number. It has the information you said plus serial number. It says 25hp ELH. But I just looked at boats.net. Looks like the 25 hp ELH is possibly 1025311VD. I'll look around the motor to verify.

https://www.boats.net/parts/search/Merc/Mercury/1999/parts.html
 
Yea that's where I found the number, I just want to check on the motor before I order anything. I don't see the carb rebuild kit on boats.net. I found it on crowleymarine.com for $73.

Thanks again!
 
I didn't see any bar codes on the engine. Only the sticker on the right that gives serial number, Hp, year, max rpm etc. and under the cover another sticker that gave some specs like timing and idle rpms.
 
Jay415 said:
I didn't see any bar codes on the engine. Only the sticker on the right that gives serial number, Hp, year, max rpm etc. and under the cover another sticker that gave some specs like timing and idle rpms.


I'll take some photos tomorrow of my engine where the numbers are located. If you've got the serial number then you can find it pretty easy, I'll copy it and see if I can hunt it down
 
Here's a Sierra kit for $11 cheaper. Not sure what brand the one you're looking at is.
https://www.wholesalemarine.com/p/1395-8237072/Repair+Kit-Carb,+Mercury+-+Mercruiser+1395-8237072.html
 
Found it on boats.net. It's #16 on the schematic part number 823707 2 REPAIR KIT for $59. Same as Crowley for $73. I just ordered that and the water pump kit. Might as well change the impeller, who knows how old it is! Same one you listed also JMichael. Thanks for your help guys! I'll update after the rebuild.
 
Jay415 said:
Found it on boats.net. It's #16 on the schematic part number 823707 2 REPAIR KIT for $59. Same as Crowley for $73. I just ordered that and the water pump kit. Might as well change the impeller, who knows how old it is! Same one you listed also JMichael. Thanks for your help guys! I'll update after the rebuild.

If you've got any questions durning the rebuild just hop on here and post photos and I'll help you out! It's pretty simple once you get the hang of it!
 

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